360 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



lateral membrane narrow, a slijjht fringe in young examples; adambulacral comb 

 with five to seven webbed spines, the three or four outer subequal and longest; 

 five to seven oral spines (usually six), both series united by continuous membrane; 

 suboral spine heavier and longer than inner marginal oral, but slender; madre- 

 poric body with a tuft of sjiines. 



Description. — The general form is somewhat variable, but the animal is very 

 stout, and the abactinal membrane is more or less inflated, the creature resembling 

 a stellate cushion. Supradorsal membrane thick, tough, and spongy, regularly 

 reticulated, the quadrate or hexagonal areas in most individuals being better differ- 

 entiated on sides of ray, and there containing twenty to thirty-five spiracula. No 

 spicules in supradorsal membrane. Surface of membrane either smooth, or rough- 

 ened and papillated by the paxillar spines. Very small specimens are relatively 

 much rougher (though not invariabh' so) than the large ones, depending, probably, 

 on the contraction of the membrane at death. (See " Variations," on p. 361.) Pseu- 

 dopaxillse very numerous, with a rather low pedicel which is shorter than the spines. 

 Spines numerous, about twenty-six in full-sized specimens; of these, seven or eight 

 thicker ones form a diverging group on the periphery, the rest being much slenderer, 

 and delicate, and occup3'ing the center. The membrane in which the spines are 

 immersed forms seven or eight laminiB radiating from the center of the group and 

 ending with each of the seven or eight peripheral spines. All spines are rather 

 stouter at the distal end. The muscle bands, wliich show as reticulations exteriorly, 

 hang down on the inner side of the supradorsal membrane like tiny partitions or cur- 

 tains, so that the "ceiling" of the nidamental cavity is fenestrated. The seven or 

 eight (fewer in small specimens) radiating spines with their laminfe of membrane 

 rise in a quite regular manner and join these so that the appearance is that of a 

 groined vault in miniature. Length of pedicel, about 2 mm.; length of spines, 

 about 3 mm. Osculum conspicuous with a raised border. 



Ambulacra narrow; feet large in two rows. Adambulacral combs, close 

 together, in large specimens with seven spines (proximally at least), or six in medium- 

 sized and small examples (five in some very small ones). Membrane slightly emar- 

 ginatcd between spines, the four or five outer of which have swollen sacculated 

 tips; the three or four outer subecjual; the third from inner end sliglitly shorter, 

 the second about half as long as third, and tlie first very short and placed aborally to 

 the series. Occasionally five spines are long and subequal (in a series of seven), but 

 four is the usual number, in large and medium-sized examples, and three in small 

 ones. Outermost spine close to actinolateral membrane with which it is joined by 

 membrane; aperture a little over half length of outer spine, the papilla narrow and 

 with free aboral edge. 



Mouth spines five to seven, usually six, the outer very short and the rest grad- 

 ually lengthening to the inner, which is slightly longer than interradial diameter of 

 plate; the whole ten to fourteen of each angle are united by a common membrane 

 to tips. Suboral spine heavier and longer than any marginal spine, slender, 

 subcylindrical, clear-tipped, pointed, and incased in heavy membrane. 



